The aim of the present study was to compare the performance of hospital clinics with and without adjunct mobile services for the delivery of secondary prevention for caries in Thai schoolchildren. A dental survey was conducted in schools served by different dental services. 711 schoolchildren were selected from primary schools in Southern Thailand by multistage cluster random sampling. WHO basic oral health survey methods were employed to evaluate three outcomes of secondary prevention: 1) Coverage of secondary prevention - all filled teeth (FT+D(F)T) among caries experienced teeth (DMFT), 2) Effectiveness of secondary prevention - successfully filled teeth (FT) among all filled teeth (FT+D(F)T) and 3) Protective effect of secondary prevention- successfully filled teeth (FT) among caries experienced teeth (DMFT). The respective percentages were 74.3, 97.5 and 72.5 in the children served by hospital-only services, and 41.3, 97.2 and 40.2 in the other group. From clustered logistic regression modeling, only the first and third outcomes were significantly different between the two access groups. This study showed that adjunct mobile service may be less effective in secondary prevention.